GB2155650A

GB2155650A - Controlled exposure

Info

Publication number: GB2155650A
Application number: GB08503115A
Authority: GB
Inventors: Hiroshi Echizen; Akiyoshi Suzuki
Original assignee: Canon Inc
Current assignee: Canon Inc
Priority date: 1984-02-14
Filing date: 1985-02-07
Publication date: 1985-09-25
Also published as: DE3504938A1; GB2192467B; GB2192467A; GB2155650B; GB8503115D0; DE3504938C2; GB8719915D0

Abstract

In a step-and-repeat wafer exposure process using chopped continuous or pulsed laser light (eg excimer laser light), each exposure is effected in two parts, viz a first coarse exposure of comparatively large preset energy and a second fine exposure of comparatively small preset energy, the amount of the second exposure being calculated in dependence on the amount of the first exposure as measured during the first exposure using a semi-transparent mirror (3, Fig. 1), measuring device (7), and control and memory unit (8). The first coarse exposure may comprise one or more pulses. In the second fine exposure, the output setting of the light source may be adjusted; alternatively, an ND filter or a diaphragm may be employed. The invention substantially overcomes the problem of deviation of energy output from a preset value. As shown, a plurality of first part coarse exposures are followed by a plurality of second part fine exposures. <IMAGE>

Description

SPECIFICATION Method and apparatus for exposure BACKGROUND OF THE INVENTION This invention relates to an exposure method and an exposure apparatus using pulsed light or intermittent light. More particularly, it relates to an exposure method and an exposure apparatus for use in the manufacture of semiconductor circuit devices.

In an optical lithography which is a technique for transferring a minute pattern of an integrated circuit onto a wafer surface, an exposure apparatus providing a higher resolution has been required.

In general, the resolving power increases in inverse proportion to the wavelength of light used in the exposure. For this reason, an optical lithography using a shorter wavelength of light is desirable.

In another aspect, reduction of the exposure time has been desired to achieve a higher throughput of the apparatus. In this connection, a super Hg lamp or an Xe-Hg lamp, which has conventionally been used as a light source providing an exposing beam, is not so advantageous because it has substantially no directionality and a low luminance.

It has recently been found that a highpower and high-luminance laser oscillatingly emitting a beam in a short wavelength region (deep UV region) is effective to be applied to the exposure apparatus. An example of such laser is an excimer laser. The excimer laser intermittently emits a laser beam at the repetition-frequency of approx, 200-300 Hz. The emission time (the duration of each pulse) is about 10-30 nsec. Because of the high power of the excimer laser, only one pulse emission is usually effective to provide a sufficient amount of exposure relative to an ordinary resist material. Therefore, the exposure time of the order of 0.01 sec. is attainable.

However, the pulse energy of the excimer laser contains fluctuation of about f 5%. This pulse energy fluctuation directly leads to irregularity in the exposure energy to be applied to chip areas on the wafer. The irregular exposure produces serious effects on the resolving power and the reproducibility of line width after development of the resist material and, therefore, decreases yield of chips.

SUMMARY OF THE INVENTION It is accordingly a primary object of the present invention to provide an exposure method and an exposure apparatus assuring uniform exposure as well as achieving an increased throughput.

It is another object of the present invention to provide an exposure method and an exposure apparatus using pulsed light or intermittent light, in which the irregularity in the amount of exposure due to the fluctuation in the exposure energy is suppressed so that the yield is increased while the throughput is improved .

Briefly, according to the present invention, there are provided a method and an apparatus for performing exposure with pulsed light or intermittent light, in which the exposure is effected by a combination of primary of coarse exposure and secondary or fine exposure. The coarse exposure is adapted to provide an amount of exposure smaller than a correct amount of exposure, while the fine exposure is adapted to provide a controlled amount of exposure smaller than that provided by the coarse exposure, whereby the entire amount of exposure becomes equal to or substantially equal to the correct amount of exposure.

These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic and diagrammatic view showing a projection type exposure apparatus according to an embodiment of the present invention.

Figure 2 is a schematic and diagrammatic view showing a proximity type exposure apparatus according to another embodiment of the present invention.

Figures 3 and 4 are schematic views, respectively, showing the magnitude relation between the energy for correct exposure and the pulse energy for the combined coarse and fine exposure according to the present invention.

Figure 5 is a schematic and diagrammatic view showing a step-and-repeat type exposure apparatus according to a further embodiment of the present invention.

Figures 6 and 7 are schematic views, respectively, showing examples of a combined coarse and fine exposure according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODI MENTS Figs. 1 and 2 show projection type and proximity type exposure apparatuses, respectively, to which the present invention is applied. In Figs. 1 and 2, corresponding elements are shown with the same reference numerals.

In Fig. 1, the exposure apparatus includes a light source 1 such as an excimer laser adapted to intermittently emit an exposing beam, an optical unit 2 for introducing the light beam emitted from the light source 1, a flat mirror 3 for deflecting the light beam introduced by the optical unit 2, and a projection lens 5 for transferring the pattern of a mask 4 onto a wafer 6 positioned on a pattern transfer plane. The exposure apparatus further includes a light measuring device 7 such as an integrating exposure meter for measuring the energy of the pulsed light. The measuring device 7 is arranged to receive pulses of light emitted from the light source 1 and transmitted through a semi-transmitting portion formed in the flat mirror 3 to monitor the quantity of pulsed light.In response to the reception of light, the measuring device 7 produces an output signal which is supplied to a pulse energy controlling unit 8. In accor dance with the output signal supplied from the measuring device 7, the control unit 8 controls the light source 1 so that an appropri ate pulse energy is emitted therefrom.

Since Fig. 2 embodiment has substantially the same structure as of Fig. 1 embodiment except that it is of proximity type as compared with the projection type of Fig. 1 embodi ment, a further description on Fig. 2 structure will be omitted here merely for the sake of simplicity of explanation.

Control of the amount of exposure accord ing to the present invention will now be described with reference to Figs. 3 and 4.

Briefly, according to the present invention, exposure of one shot is effected by a combi nation of a primary or coarse exposure and a secondary or fine exposure. At least two pulses emitted from the light source 1 are used for the coarse and fine exposures. The coarse exposure is adapted to provide an amount of exposure which is smaller than a correct exposure amount, while the fine expo sure is adapted to provide an amount of exposure which is much less than that pro vided by the coarse exposure. Fig. 3 shows an example of two-pulse exposure, while Fig. 4 shows an example of four-pulse exposure. For the sake of best understanding of the present invention, description will be made first to the Fig. 3 example of two-pulse exposure.

Upon exposure of one shot, as is shown in Fig. 3, the primary or coarse exposure is first effected with one pulse emitted from the light source 1 and having a pulse energy E, which is approx. 80-90% of an energy Eo necessary for providing a correct exposure amount. Pre ferably, the proportion or magnitude of the pulse energy E, is selected while taking into account that the pulse energy to be provided by the light source fluctuates in the range of i f 5%, as described in the foregoing.

The pulse energy E, is detected by the measuring device 7. Actually, the magnitude of the pulse energy E1 is calculated out on the basis of the portion of the pulse energy E1 transmitted through the flat mirror 3 and of the transmitting factor of the flat mirror 3.

After the magnitude of the pulse energy E1 is detected, the difference between the correct exposure energy Eo and the pulse energy E1 is detected by the control unit 8. On the basis of the thus detected difference, the control unit 8 controls the light source 1, such that a second pulse for the fine exposure and having a pulse energy E2 corresponding to the differential energy Eo-E1 is emitted from the light source 1. In the magnitude relation, the pulse energy E2 is smaller than the pulse energy E which is smaller than the correct exposure energy EO.

The adjustment of the pulse energy E2 is effected in Fig. 1 or 2 embodiment by controlling the output itself of the light source 1. The pulse energy E2 may however be controlled by means of an ND filter or a diaphragm mechanism inserted into the optical path of the light source 1.

The combination of coarse and fine exposure as described in the foregoing assures regular and stable exposure for every shot of exposure.

More specifically, the pulse energy E2 for the fine exposure is much less than the correct exposure energy EQ. This means that the absolute deviation, caused by the + 5% fluctuation, in the actually produced pulse energy E2 is extremely small as compared with the magnitude of the correct exposure energy Eo.

Therefore, the total amount of pulse energies E1 + E2 can be very close to the correct exposure energy EO, even if the pulse energy E2 contains, e.g., + 5% fluctuation. Thus, the present invention stably assures the amount of exposure which is equal to or substantially equal to the correct exposure amount for every shot of exposure.

This will be best understood in comparison with the effects of j 5% fluctuation in the one-shot/one-pulse exposure wherein the exposure of each shot is effected by one pulse.

In the one-shot/one-pulse exposure, the fluctuation of, e.g. + 5% in the pulse output would directly cause + 5% over-exposure as compared with the correct exposure energy EO. The absolute amount of the excess + 5% of the correct exposure energy EO is substantially greater than the absolute amount of the 5% deviation of the pulse energy E2.

In order to positively establish the relation that the pulse energy E2 is much less than the correct exposure energy E0, the magnitude of the pulse energy E1 for the coarse exposure is preferably determined so as to satisfy the relation: E2 E1 < EO In the combined coarse and fine exposure according to the present invention, the number of pulse exposures is in fact larger than that of the one-shot/one-pulse exposure.

Since, however, the pulse emission time (the duration of each pulse) is of the order of 0.01 sec. as described in the foregoing and also since the number of pulses for the coarse and fine exposures is held minimum (two in Fig. 3 example), the exposure time is very short so that a high throughput can be kept.

If the resist material on the wafer requires a large amount of exposure energy to achieve the correct exposure, the primary or coarse exposure is effected by a plural number of pulse exposures (e.g. three such as shown in Fig. 4) through a corresponding number of pulses each having a pulse energy E1. After the plural number of pulse exposures for the coarse exposure are completed, the fine exposure is effected with a pulse energy E21 which is controlled so that the total amount of pulse energies E1 + E1 + E, + E21 is within a tolerable range of the correct exposure energy Eol, e.g. within 100 + 3%.

In this manner, a minimum number of pulse exposures is appropriately selected in accordance with the magnitude of correct exposure energy, while the magnitude relation between the pulse energies for the coarse and fine exposures is determined such that the amount of exposure to be provided by the fine exposure is much less than that to be provided by the coarse exposure. By this, the amount of exposure can be controlled precisely and stably, and a high throughput is assured.

The pulse-oscillation type laser may, of course, be replaced by a continuous emission type laser. In such case, suitable chopper means such as a shutter, an ND filter, etc.

may be used to repeatedly intermit the light from the source, whereby substantially the same effects are attainable as in the case of the pulsed laser beam.

Fig. 5 shows a step-and-repeat type exposure apparatus, called a stepper, to which the present invention is applied.

As is shown in Fig. 5, the exposure apparatus includes a light source 1, an optical unit 2, a flat mirror 3, a measuring device 7 and a control unit 8 all of which are substantially the same as the corresponding elements, respectively, of Fig. 1 embodiment. The exposure apparatus of Fig. 5 embodiment further includes a reduction projection optical system 5' disposed between a mask 4 and a wafer 6.

The wafer 6 is carried by a carriage 9 which is adapted to be continuously moved by an unshown drive source.

In the exposure operation, the light source 1 such as an excimer laser intermittently emits the exposure light. Simultaneously therewith, the carriage 9 is continuously moved by the unshown drive source at a speed which is coordinated with the emission of pulses from the light source. The continuous movement of the carriage 9 has an advantage over the conventional stepwise movement in a traditional stepand-repeat system, because the former is effective to delete any time loss owing to the repetition of stop and re-start of movement of the carriage 9. Consequently, the throughput of the apparatus is increased.

Fig. 6 shows an example of the exposure sequence employed in the Fig. 5 embodiment.

In Fig. 6, reference characters C,-C5 denote rows, respectively, each containing a plurality of chip areas. In this embodiment, each row contains three or five chip areas. In each of the chip areas shown in Fig. 6, the dot designates irradiation of laser pulse or pulses for the coarse exposure, while the circle designates irradiation of laser pulse for the fine exposure.

For the sake of best understanding of the present invention, description will be made to two-pulse exposure for the combined coarse and fine exposure, i.e. the combination of coarse exposure by one pulse.

If the exposure sequence is arranged such that the coarse exposure and the subsequent fine exposure are effected relative to one chip area and thereafter the wafer is stepped to effect the coarse and fine exposures relative to the succeeding chip area, there would be a substantial time loss due to the repetition of stop and re-start of movement of the carriage 9 as described in the foregoing. In view of this, the exposure sequence according to the present embodiment is arranged such that a plurality of chip areas are grouped into one (e.g. C,) and the coarse exposures are successively and sequentially effected to the chip areas in the one group and thereafter the fine exposures are successively and sequentially effected to the chip areas in that one group.

This exposure process will hereinafter be referred to as "complete step" or "one complete step". After the complete step relative to one of the groups is finished, the complete step is repeated relative to each of the remain- ing groups.

More specifically, as shown in Fig. 6, successive and sequential coarse exposures denoted by dots are first effected relative to the chip areas in the row C, in the order designated by arrows. During these coarse exposures, the pulse energy applied to each of the chip areas is detected and the differential energy between the correct exposure energy and the thus detected pulse energy, with respect to each of the chip areas, is calculated and stored by the control unit 8. Subsequently, successive and sequential fine exposures as denoted by circles are effected relative to the chip areas in the row C, in the reverse order as designated by arrows, with the pulse energies controlled by the control unit 8. By this, one complete step relative to the row C, is finished.

Subsequently, in the order as denoted by arrows shown in Fig. 6, successive coarse exposures and successive fine exposures are effected relative to the chip areas in each of the rows C2-C5, sequentially.

As described with reference to Fig. 3, the pulse energy for the coarse exposure relative to each of the chip areas is selected so that it is, e.g., approx. 80-90% of the correct exposure energy, while the pulse energy for the fine exposure is controlled to provide the remaining exposure energy. The selection or control of the pulse energy can be achieved by controlling the light source 1 through the control unit 8. The divided application of exposure energy as described above assures precise control of the amount of exposure.

That is, according to the present invention, the fine exposure is effected by a pulse energy which is much less than the correct exposure energy. Therefore, any fluctuation of the pulse energy for the fine exposure will cause merely an absolute amount of deviation which is extremely small as compared with the magnitude of the correct exposure energy.

While, in Fig. 6 example, the exposure of the entire wafer is complete steps, the fivestep exposure may be replaced by one-step exposure, i.e. the combination of one complete series of successive coarse exposures with one complete series of successive fine exposures; such as shown in Fig. 7.

More specifically, if the stepper is provided with an alignment system of off-axis type, coarse exposures are successively and sequentially effected relative to all the chip areas on the wafer, with the movement of the wafer being executed while relying on the precision of the laser interferometer in the alignment system. During these coarse exposures, each of the actually produced pulse energies is detected by the measuring device 7 and the magnitude of the pulse energy necessary for supplementing the coarse exposure relative to each of the chip areas is calculated and stored in the control unit 8.After all the coarse exposures are completed, fine exposures are successively and sequentially effected relative to all the chip areas on the wafer, with the pulse energy of each fine exposure being appropriately controlled in accordance with the magnitude of the pulse energy of the coarse exposure. With this arrangement, efficient exposure as well as regular and stable exposure are attainable.

While, in Fig. 7 example, the fine exposures are effected in the same order as the coarse exposures, this may be reversed. Further, the off-axis alignment system may, of course, be replaced by a TTL (through the lens) alignment system. Since the operation in such case is essentially the same as the Fig. 7 example, description thereof will be omitted here for the sake of simplicity of explanation.

In the examples of Fig. 6 and 7, the coarse exposure may of course be effected by a plural number of pulse exposures.

While, in the foregoing embodiment, the present invention has been described with reference to exposure apparatuses of projection type and proximity type, the invention is not limited thereto and also is applicable to a contact type exposure apparatus. In addition thereto, the present invention is applicable to the control of exposure in a case where a pulse-oscillation type laser such as the excimer laser is employed as a light source for a recently developed resistless etching.

In accordance with the present invention, as has hitherto been described, the combined coarse and fine exposure assures precise and stable control of the amount of exposure while ensuring improvements in the throughput.

Moreover, in a case where the invention is applied to a step-and-repeat type exposure apparatus, coarse exposures are successively and sequentially effected relative to a plurality of chip areas and thereafter fine exposures are successively and sequentially effected relative to the same chip areas. By this, the stage carrying thereon the wafer can be moved continuously without repetition of stoppage for every chip area, whereby the time loss due to the repetition of stop and re-start is removed. Thus, the throughput is further increased.

While the invention has been described with reference to the structures disclosed herein, it is not confined to the details set forth and this application is intended to cover such modifications or changes as may come within the purposes of the improvements or the scope of the following claims.

Claims

1. A method of performing exposure with intermittent light, comprising: effecting a coarse exposure to provide an amount of exposure smaller than a correct exposure amount; and effecting a fine exposure to provide an amount of exposure smaller than that provided by said coarse exposure, said fine exposure being controlled so that the total amount of exposure provided by said coarse exposure and fine exposure being equal to or approximately equal to the correct exposure amount.

2. A method according to Claim 1, wherein plural times of exposures are effected for said coarse exposure.

3. A method according to Claim 1, wherein the intermittent light is provided by an excimer laser.

4. A method of performing exposure with intermittent light, comprising: sequentially effecting plural times of coarse exposures relative to a plurality of areas to be exposed, each of said coarse exposures providing an amount of exposure smaller than a correct exposure amount on the corresponding one of the areas to be exposed; and sequentially effecting plural times of fine exposures relative to the areas to be exposed, each of said fine exposures providing an amount of exposure which is smaller than that provided by said coarse exposure for the corresponding one of the areas to be exposed and which supplements said coarse exposure so that the total amount of exposure provided by said coarse exposure and fine exposure becomes equal to or approximately equal to the correct exposure amount.

5. A method according to Claim 4, wherein plural times of exposures are effected for said coarse exposure for each of the areas to be exposed.

6. A method according to Claim 4, wherein the order of said fine exposures relative to the areas to be exposed is the same as that of said coarse exposures.

7. A method according to Claim 4, wherein the order of said fine exposures relative to the areas to be exposed is opposite to that of said coarse exposures.

8. A method according to Claim 4, wherein the intermittent light is provided by an excimer laser.

9. An exposure apparatus, comprising: means for producing intermittent light; measuring means for integratingly detecting an amount of exposure on a surface to be exposed; and control means for effecting a coarse exposure and a fine exposure relative to the surface to be exposed, said control means controlling said coarse exposure so that it provides an amount of exposure smaller than a correct exposure amount of the surface to be exposed, said control means also controlling said fine exposure so that it provides an amount of exposure smaller than that provided by said coarse exposure and so that the total amount of exposure provided by said coarse exposure and fine exposure becomes equal to or approximately equal to the correct exposure amount.

10. An apparatus according to Claim 9, wherein said means for producing intermittent light comprises an excimer laser.

11. An exposure apparatus, comprising: means for producing intermittent light; a a projection optical system for transferring a pattern of a mask onto a wafer; carriage means for carrying thereon the wafer, said carriage means being movable to transfer the pattern of the mask onto a plurality of areas on the wafer; measuring means for integratingly detecting an amount of exposure on each of said areas on the wafer; and control means for effecting a coarse exposure and a fine exposure relative to each of said areas on the wafer, said control means controlling said coarse exposure so that it provides an amount of exposure smaller than a correct exposure amount of each of said areas on the wafer, said control means also controlling said fine exposure so that it provides an amount of exposure smaller than that provided by said coarse exposure relative to the corresponding one of said areas on the wafer and so that the total amount of exposure provided by said coarse exposure and fine exposure relative to the corresponding one of the area on the wafer becomes equal to or approximately equal to the correct exposure amount.

12. An apparatus according to Claim 11, wherein said means for producing intermittent light comprises an excimer laser.

13. An apparatus according to Claim 11, wherein said carriage means is movable continuously.

14. An apparatus according to Claim 11, wherein the integratingly detected amount of exposure on each of the areas of the wafer provided by said coarse exposure is memorized in said control unit, and said fine exposure is controlled in accordance with the memorized amount of exposure by said coarse exposure.

15. Exposure apparatus substantially as herein described with reference to any of the accompanying drawings.

16. An exposure method substantially as herein described with reference to any of the accompanying drawings.